Semiconductor device and manufacturing method thereof

ABSTRACT

Provided is an in-wiring-layer active element (component) which allows for electrical isolation between a gate electrode and a channel in a top gate structure. A semiconductor device includes a first wiring layer, a second wiring layer, and a semiconductor element. The first wiring layer has a first interlayer insulating layer, and a first wire embedded in the first interlayer insulating layer. The second wiring layer has a second interlayer insulating layer, and second wires embedded in the second interlayer insulating layer. The semiconductor element is provided at least in the second wiring layer. The semiconductor element includes a semiconductor layer provided in the second wiring layer, a gate insulating film provided in contact with the semiconductor layer, a gate electrode provided on the opposite side of the semiconductor layer via the first gate insulating film, and a first side wall film provided over a side surface of the semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2012-195291 filed onSep. 5, 2012 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a semiconductor device, and can be usedappropriately for a semiconductor device having, e.g., an active element(component) in a wiring layer.

A technique which provides an active element (component) in a wiringlayer in a semiconductor device has been known. The active element(component) allows the function of such a semiconductor device to bechanged without involving a change in the layout of semiconductorelements formed over a semiconductor substrate. Therefore, it ispossible to manufacture a plurality of types of semiconductor deviceshaving different functions using the semiconductor substrate, whilekeeping the same layout of the semiconductor elements over thesemiconductor substrate. In this case, the manufacturing cost of thesemiconductor devices can be reduced.

For example, a semiconductor device and a manufacturing method of thesemiconductor device are disclosed in Japanese Unexamined PatentPublication No. 2010-141230 (corresponding US Patent ApplicationPublication No. 2010/148171 (A1)). The semiconductor device includes asemiconductor substrate, a first wiring layer, a semiconductor layer, agate insulating film, and a gate electrode. The first wiring layerincludes an insulating layer formed over the semiconductor substrate,and first wires embedded in the surface of the insulating film. Thesemiconductor layer is located over the first wiring layer. The gateinsulating film is located over or under the semiconductor layer. Thegate electrode is located on the opposite side of the semiconductorlayer via the gate insulating film. At this time, the semiconductorlayer, the gate insulating film, and the gate electrode form atransistor as an active element (component). It is possible to use,e.g., one of the first wires as the gate electrode. It is also possibleto use, e.g., a diffusion preventing film in the first wiring layer asthe gate insulating film. In that case, the gate insulating film isformed under the semiconductor layer. The semiconductor device has aso-called bottom-gate element structure. The semiconductor device canfurther include a charge trap film, and a back-gate electrode over thesemiconductor layer. In this case, the semiconductor device basicallyhas a bottom-gate element structure, which is a double-gate elementstructure auxiliarily also including the gate opposing the bottom gate.

As a related-art technology, a technique for a semiconductor device isdisclosed in Japanese Unexamined Patent Publication No. 2009-94494(corresponding US Patent Application Publication No. 2009/078970 (A1)).In the semiconductor device, over a substrate having an insulatingsurface, a plurality of field effect transistors are stacked withrespective interlayer insulating layers interposed therebetween. Thesemiconductor layers included in the plurality of field effecttransistors are isolated from each other by the semiconductor substrate.The semiconductor layers are joined with the substrate having theforegoing insulating surface or with respective insulating layersprovided over the foregoing interlayer insulating layers. The pluralityof field effect transistors are each covered with an insulating filmwhich gives a strain to each of the semiconductor layers.

A manufacturing method of a semiconductor device, the semiconductordevice, an electrooptical device, and an electronic device are disclosedin Japanese Unexamined Patent Publication No. 2009-283819. In themanufacturing method of the semiconductor device, a plurality ofsemiconductor films are laminated. The manufacturing method of thesemiconductor device includes five steps. The first step is the step offorming a plug electrode including carbon nanotube over the firstsemiconductor film. The second step is the step of forming an interlayerinsulating film around the formed plug electrode. The third step is thestep of planarizing the surface of the interlayer insulating film toexpose the top portion of the plug electrode. The fourth step is thestep of forming the amorphous second semiconductor film over theinterlayer insulating film and the top portion of the plug electrode.The fifth step is the step of supplying energy to the amorphous secondsemiconductor film to cause the exposed plug electrode to function as acatalyst and crystallize the amorphous second semiconductor film.

As a related-art technology, an LSI is disclosed in Non-Patent Document1 (2012 Symposium on VLSI Technology digest of Technical Papers, 123-124(2012)) in which an oxide semiconductor layer is incorporated in amultilayer interconnect layer. Also, as a related-art technology, a CMOScircuit using an oxide semiconductor layer is disclosed in Non-PatentDocument 2 (2011 Symposium on VLSI Technology Digest of TechnicalPapers, 120-121 (2011)). Also, as a related-art technology, a transistordevice structure using an oxide semiconductor layer is disclosed inNon-Patent Document 3 (2011 IEEE International Electron Devices Meeting(IEDM), 155-158 (2011)).

RELATED ART DOCUMENTS Patent Documents Patent Document 1

-   Japanese Unexamined Patent Publication No. 2010-141230

[Patent Document 2]

-   Japanese Unexamined Patent Publication No. 2009-094494

[Patent Document 3]

-   Japanese Unexamined Patent Publication No. 2009-283819

Non-Patent Documents Non-Patent Document 1

-   K. Kaneko et al., “Operation of Functional Circuit Elements using    BEOL-Transistor with InGaZnO Channel for On-chip High/Low Voltage    Bridging I/Os and High-Current Switches”, 2012 Symposium on VLSI    Technology Digest of Technical Papers, 123-124 (2012).

[Non-Patent Document 2]

-   K. Kaneko et al., “A Novel BEOL-Transistor (BETr) with InGaZnO    Embedded in Cu-Interconnects for On-chip High Voltage I/Os in    Standard CMOS LSIs”, 2011 Symposium on VLSI Technology Digest of    Technical Papers, 120-121 (2011).

[Non-Patent Document 3]

-   K. Kaneko et al., “High Reliable BEOL-Transistor with    Oxygen-controlled InGaZnO and Gate/Drain Offset Design for High/Low    Voltage Bridging I/O Operations”, 2011 IEEE International Electron    Devices Meeting (IEDM), 155-158 (2011).

SUMMARY

In Japanese Unexamined Patent Publication No. 2010-141230 mentionedabove, the transistor as the in-wiring-layer active element (component)has the bottom-gate element structure or the double-gate elementstructure based on the bottom-gate element structure. This leads toseveral structural problems. For example, a gate electrode normallyneeds to have such a structure as to extend completely across asemiconductor layer. However, in providing the transistor of JapaneseUnexamined Patent Publication No. 2010-141230 mentioned above with sucha structure, the following problem is encountered. In the case ofsimultaneously forming the semiconductor layer and the gate insulatingfilm and then forming the gate electrode, at the side surfaces of theends of the semiconductor layer, the gate electrode undesirably comes incontact with the semiconductor layer. In the case of forming thesemiconductor layer and then simultaneously forming the gate insulatingfilm and the gate electrode also, the gate insulating film is thinned atthe side surfaces of the ends of the semiconductor layer. As a result,it is highly possible that the gate electrode undesirably comes incontact with the semiconductor layer.

Other problems and novel features of the present invention will becomeapparent from a statement in the present specification and theaccompanying drawings.

In an embodiment, a semiconductor element (active element (component))having a top-gate element structure is provided in a wiring layer in asemiconductor device. Over side surfaces of a semiconductor layer in thesemiconductor element (active element (component)), side wall films(sidewalls) other than an interlayer insulating film are provided.

According to the embodiment, there are the side wall films at positionswhere a gate electrode extends across the semiconductor layer. This canprevent contact between the gate electrode and the semiconductor layerand provide electrical isolation between the gate electrode and thesemiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view showing an example of a configurationof a semiconductor device according to a first embodiment;

FIG. 1B is a cross-sectional view showing the example of theconfiguration of the semiconductor device according to the firstembodiment;

FIG. 2 is a plan view showing the example of the configuration of thesemiconductor device according to the first embodiment;

FIG. 3A is a cross-sectional view showing an example of a manufacturingmethod of the semiconductor device according to the first embodiment;

FIG. 3B is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3C is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3D is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3E is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3F is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3G is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3H is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3I is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 3J is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the firstembodiment;

FIG. 4 is a cross-sectional view showing a first modification of theconfiguration of the semiconductor device according to the firstembodiment;

FIG. 5A is a cross-sectional view showing a second modification of theconfiguration of the semiconductor device according to the firstembodiment;

FIG. 5B is a cross-sectional view showing a third modification of theconfiguration of the semiconductor device according to the firstembodiment;

FIG. 6A is a cross-sectional view showing an example of a configurationof a semiconductor device according to a second embodiment;

FIG. 6B is a cross-sectional view showing another example of theconfiguration of the semiconductor device according to the secondembodiment;

FIG. 7 is a plan view showing the example of the configuration of thesemiconductor device according to the second embodiment;

FIG. 8A is a cross-sectional view showing an example of a manufacturingmethod of the semiconductor device according to the second embodiment;

FIG. 8B is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the secondembodiment;

FIG. 8C is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the secondembodiment;

FIG. 8D is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the secondembodiment;

FIG. 8E is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the secondembodiment;

FIG. 9 is a cross-sectional view showing an example of a modification ofthe configuration of the semiconductor device according to the secondembodiment;

FIG. 10 is a cross-sectional view showing an example of a configurationof a semiconductor device according to a third embodiment;

FIG. 11 is a cross-sectional view showing a modification of theconfiguration of the semiconductor device according to the thirdembodiment;

FIG. 12 is a cross-sectional view showing a configuration of asemiconductor device according to a fourth embodiment;

FIG. 13 is a plan view showing the configuration of the semiconductordevice according to the fourth embodiment;

FIG. 14A is a cross-sectional view showing an example of a manufacturingmethod of the semiconductor device according to the fourth embodiment;

FIG. 14B is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14C is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14D is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14E is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14F is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14G is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14H is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14I is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 14J is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fourthembodiment;

FIG. 15 is a cross-sectional view showing an example of a configurationof a semiconductor device according to a fifth embodiment;

FIG. 16 is a plan view showing the example of the configuration of thesemiconductor device according to the fifth embodiment;

FIG. 17A is a cross-sectional view showing an example of a manufacturingmethod of the semiconductor device according to the fifth embodiment;

FIG. 17B is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 17C is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 17D is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 17E is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 17F is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 17G is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 17H is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to the fifthembodiment;

FIG. 18 is a cross-sectional view showing an example of a configurationof a semiconductor device according to a sixth embodiment;

FIG. 19 is a plan view showing the example of the configuration of thesemiconductor device according to the sixth embodiment;

FIG. 20 is a cross-sectional view showing an example of a configurationof a semiconductor device according to a seventh embodiment;

FIG. 21A is a cross-sectional view showing an example of a manufacturingmethod of the semiconductor device according to the seventh embodiment;

FIG. 21B is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to theseventh embodiment;

FIG. 21C is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to theseventh embodiment;

FIG. 21D is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to theseventh embodiment;

FIG. 21E is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to theseventh embodiment;

FIG. 21F is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to theseventh embodiment;

FIG. 21G is a cross-sectional view showing the example of themanufacturing method of the semiconductor device according to theseventh embodiment;

FIG. 22 is a cross-sectional view showing an example of a configurationof a semiconductor device according to an eighth embodiment;

FIG. 23 is a cross-sectional view showing an example of a configurationof a semiconductor device according to a ninth embodiment;

FIG. 24 is a plan view showing the example of the configuration of thesemiconductor device according to the ninth embodiment;

FIG. 25 is a cross-sectional view showing an example of a configurationof a semiconductor device according to a tenth embodiment;

FIG. 26 is a plan view showing the example of the configuration of thesemiconductor device according to the tenth embodiment;

FIG. 27 is a cross-sectional view showing an example of a configurationof a semiconductor device according to an eleventh embodiment; and

FIG. 28 is a layout chart schematically showing an example of aconfiguration of a semiconductor device according to a twelfthembodiment.

DETAILED DESCRIPTION

Hereinbelow, a description will be given of a semiconductor device and amanufacturing method of the semiconductor device according to each ofembodiments with reference to the accompanying drawings.

First Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the first embodiment. FIGS. 1A, 1B, and 2 arecross-sectional views and a plan view each showing an example of theconfiguration of the semiconductor device according to the presentembodiment. Note that FIGS. 1A and 1B show cross sections each along theline A-A′ of FIG. 2, and FIG. 1A shows the main portion of FIG. 1B.

A semiconductor device 100 of the present embodiment includes a firstwiring layer 150, a second wiring layer 170, and a semiconductor element200. The first wiring layer 150 has a first interlayer insulating layer152, and a first wire 164 embedded in the first interlayer insulatinglayer 152. The second wiring layer 170 has a second interlayerinsulating layer 172 formed above the first wiring layer 150, and secondwires 188, 285, and 289 each embedded in the second interlayerinsulating layer 172. The semiconductor element 200 is provided at leastin the second wiring layer 170. The semiconductor element 200 includes asemiconductor layer 220, a gate insulating film 221, a gate electrode222, and first side wall films 226. The semiconductor layer 220 isprovided in the second wiring layer 170. The gate insulating film 221 isprovided in contact with the semiconductor layer 220. The gate electrode222 is provided on the opposite side of the semiconductor layer 220 viathe gate insulating film 221. The first side wall films (226) areprovided on the side surfaces of the semiconductor layer 220. It can besaid that the semiconductor element 200 is an in-wiring-layer activeelement (component) (or in-wiring-layer functional element) provided inthe wiring layer.

By providing such a configuration, even when the gate electrode 222extends to the ends of the island-shaped semiconductor layer 220 in thesemiconductor element 200, it is possible to prevent a phenomenon inwhich the gate electrode 222 comes in direct contact with thesemiconductor layer 220 at the side surfaces of the ends of thesemiconductor layer 220. This can stabilize the operation of thesemiconductor element 200 and improve the reliability thereof. Inparticular, when the gate electrode 222 has such a structure (FIG. 2) asto extend across the island-shaped semiconductor layer 220, it ispreferable to provide the foregoing configuration.

Also, in the semiconductor element 200, the gate electrode is not thefirst wire 164 of the first wiring layer 150, but the dedicated gateelectrode 222 is provided. Therefore, the characteristics of the gateelectrode are not limited to those of a wiring material. As the gateelectrode 222, a metal material having desired characteristics can beused. As a result, there is no limit to the work function of the gateelectrode, and a threshold voltage can be set.

Also, in the semiconductor element 200, the gate insulating film is nota diffusion preventing film (e.g., a Cu diffusion preventing film) inthe second wiring layer 170, but the dedicated gate insulating film 221is provided. Therefore, the characteristics of the gate insulating filmare not limited to those of the material of the diffusion preventingfilm. As the gate electrode 222, a desired material having a desiredfilm thickness can be used. As a result, an increase in gate capacitance(i.e., a characteristic improvement) can be easily achieved.

A further description will be given below of the semiconductor device100.

The semiconductor device 100 includes a semiconductor substrate 101, acontact layer 130 provided over the semiconductor substrate 101, and awiring layer 140 provided over the contact layer 130. The semiconductorsubstrate 101 includes a semiconductor element shown by way of exampleby a transistor or a capacitive element. In the example of the drawing,a transistor 121 is formed. The transistor 121 includes source/drainelectrodes 122 and 123, a gate electrode 124, and a gate insulating film125. The transistor 121 is isolated from other elements by an isolatinglayer 120. The contact layer 130 includes an interlayer insulating layer131 provided over the semiconductor substrate 100, and contacts 142embedded in the interlayer insulating layer 131. The wiring layer 140includes an interlayer insulating layer 132 provided over the interlayerinsulating layer 131, and wires 144 embedded in the interlayerinsulating layer 132. The source/drain electrodes 122 and 123 of thetransistor 121 are coupled to the wires 144 via the contacts 142.

The first wiring layer 150 includes a cap insulating layer 151 providedover the wiring layer 140, and a first interlayer insulating layer 152provided over the cap insulating layer 151. The cap insulating layer 151prevents diffusion of the wiring material (e.g., Cu) of the wires 144.The first wiring layer 150 further includes a via 162 and the first wire164. The via 162 has the lower end thereof extending through the capinsulating layer 151 and coupled to the wire 144 and the upper endthereof coupled to the first wire 164. The first wire 164 is provided onthe top surface side of the first interlayer insulating layer 152.

The second wiring layer 170 includes a cap insulating layer 171 providedover the first wiring layer 150, and a second interlayer insulatinglayer 172 provided over the cap insulating layer 171. The cap insulatinglayer 171 prevents diffusion of the wiring material (e.g., Cu) of thefirst wire 164. The second wiring layer 170 further includes a via 189and the second wire 188. The via 189 has the lower end thereof extendingthrough the cap insulating layer 171 and coupled to the first wire 164and the upper end thereof coupled to the second wire 188. The secondwire 188 is provided on the top surface side of the second interlayerinsulating layer 172. In the example of the drawing, the via 189 and thesecond wire 188 in a dual damascene structure are shown.

The second wiring layer 170 further includes the island-shapedsemiconductor layer 220 provided over the cap insulating layer 171, thegate insulating film 221 provided over the semiconductor layer 220, thegate electrode 222 provided over the gate insulating film 221, and thesidewalls 226 provided around the semiconductor layer 220. Thesemiconductor layer 220 functions as a channel. The gate electrode 222,the gate insulating film 221, and the semiconductor layer 220 form thesemiconductor element 200 as the transistor. The gate electrode 222 hassuch a structure as to extend completely across the island-shapedsemiconductor layer 220. Consequently, the gate electrode 222 may comein contact with the side surfaces of the ends of the semiconductor layer220 at the end surfaces of the semiconductor layer 220. However, sincethe side surfaces of the semiconductor layer 222 are provided with thesidewalls 226, the phenomenon in which the gate electrode 222 comes incontact with the semiconductor layer 220 can be prevented.

The second wiring layer 170 further includes a via 290 and the secondwire 289 which are coupled to the gate electrode 222. The via 290 hasthe lower end thereof coupled to the end portion (end portion distantfrom the semiconductor layer 220) of the gate electrode 222 and theupper end thereof coupled to the second wire 289. The second wire 289 isprovided on the top surface side of the second interlayer insulatinglayer 172. In the example of the drawing, the via 290 and the secondwire 289 in a dual damascene structure are shown. The second wiringlayer 170 further includes contacts 286 as source/drain electrodes andthe second wires 285. The contacts 286 have the lower ends thereofcoupled to the semiconductor layer 220 and the upper ends thereofcoupled to the second wires 285. The second wires 285 are provided onthe top surface side of the second interlayer insulating layer 172. Inthe example of the drawing, the contacts 286 and the second wires 285 ina dual damascene structure are shown.

In other words, in the semiconductor device 100 according to the presentembodiment, the semiconductor element 200 uses the semiconductor layer(oxide semiconductor) 220 formed over the cap insulating layer (e.g., Cudiffusion preventing layer) 171 provided over the first wiring layer(e.g., Cu wiring layer) 150 as the channel. The semiconductor layer 220is patterned into an island shape and, over the end surfaces (sidesurfaces) thereof, the sidewalls 226 are formed. Over the semiconductorlayer 220, the gate insulating film 221 and the gate electrode 222 thathave been patterned are disposed. The vias coupling the first wiringlayer (Cu wiring layer) 150 to the second wires (or pad electrodes) 285are used as the source/drain electrodes (contacts 286) of thesemiconductor element 200. The source/drain electrodes (contacts 286)are disposed on both sides of the gate insulating film 221 and the gateelectrode 222. The gate electrode 222 has a shape which extends over andacross the semiconductor layer 220. However, since the side surfaces ofthe semiconductor layer 220 are protected by the sidewalls 226, the gateelectrode 222 is kept from coming in contact with the semiconductorlayer 220.

Next, a description will be given of the manufacturing method of thesemiconductor device according to the present embodiment. FIGS. 3A to 3Jare cross-sectional views each showing an example of the manufacturingmethod of the semiconductor device according to the present embodiment.Each of the drawings corresponds to a cross section along the line A-A′of FIG. 2. Note that, in FIGS. 3A to 3J, the illustration of thesemiconductor substrate 101, the contact layer 130, and the wiring layer140 is omitted.

First, as shown in FIGS. 3A to 3C, the step of forming the island-shapedsemiconductor layer 220 over the wiring layers (150 and 171) having thefirst wire 164 is performed. Then, as shown in FIG. 3D, the step offorming the insulating film (226) so as to cover the semiconductor layer220 and the wiring layers (150 and 170) therewith is performed.Subsequently, as shown in FIG. 3E, the step of etching back theinsulating film (226) to form the sidewalls 226 covering the sidesurfaces of the semiconductor layer 220 is performed. Thereafter, asshown in FIGS. 3F to 3G, the step of successively forming the first gateinsulating film 221 and the gate electrode 222 over the semiconductorlayer 220 is performed. At this time, the gate electrode 222 is formedover the first gate insulating film 221 so as to extend over thesemiconductor layer 220 and the sidewalls 226.

In the present embodiment, as shown in the steps of FIGS. 3D and 3E, thesidewalls 226 are formed over the side surfaces of the island-shapedsemiconductor layer 220. Since the sidewalls 226 cover the exposed sidesurfaces of the semiconductor layer 220, the side surfaces of thesemiconductor layer 220 are not affected by the subsequent steps.Specifically, the sidewalls 226 physically/chemically/electricallyisolate/protect the semiconductor layer 220 from the gate electrode 222,which is formed subsequently. This allows the foregoingisolating/protecting function of the sidewalls 226 to prevent aphenomenon such as the contact or reaction of the gate electrode 222with or to the semiconductor layer 220. As a result, it is possible tostabilize the operation of the semiconductor element 200 and improve thereliability thereof.

A further description will be given below of the manufacturing method ofthe semiconductor device 100 according to the present embodiment.

First, as shown in FIG. 1, the semiconductor substrate 101 is formedwith the isolating layer 120. Then, over the semiconductor substrate101, e.g., the transistor 121 is formed as the semiconductor element.Subsequently, the contact layer 130 (including the interlayer insulatinglayer 131 and the contact 142), and the wiring layer 140 (including theinterlayer insulating layer 132 and the wires (copper (Cu) wires) 144)are formed. For the foregoing steps, a conventionally known method canbe used.

Next, as shown in FIG. 3A, over the wiring layer 140 (not shown), thecap layer 151 for preventing diffusion of copper (Cu) and the firstinterlayer insulating layer 152 are deposited in this order. Examples ofthe material of the cap insulating layer 151 include silicon nitride(SiN) and silicon carbonitride (SiCN). Examples of the material of thefirst interlayer insulating layer 152 include silicon dioxide (SiO₂).Subsequently, in the first interlayer insulating layer 152, the via 162and the first wire 164 are embedded using a single damascene method or adual damascene method. In this manner, the first wiring layer 150 isformed. Examples of the material of the via 162 and the first wire 164include copper (Cu). Thereafter, the cap insulating layer 171 is formedso as to cover the first interlayer insulating film 152 and the firstwire 164. Examples of the material of the cap insulating layer 171include silicon nitride (SiN) and silicon carbonitride (SiCN). The filmthickness thereof is about 10 to 50 nm. The foregoing steps areperformed by the same method as used to form a typical semiconductordevice having a copper (Cu) wiring layer.

Next, as shown in FIG. 3B, over the cap insulating layer 171, thesemiconductor layer 220 serving as the channel of the semiconductorelement 200 is formed by, e.g., a sputtering method. Preferred examplesof the material of the channel include an InGaZnO (IGZO) layer, an InZnOlayer, a ZnO layer, a ZnAlO layer, a ZnCuO layer, an NiO layer, a SnOlayer, a SnO₂ layer, a CuO layer, a Cu₂O layer, a Ta₂O₅ layer, a TiO₂layer, a laminated structure of any two or more of the foregoing layers,and a laminated structure of any one or more of the foregoing layers andanother material. Each of the foregoing layers can be formed at arelatively low temperature which does not affect the properties of thewiring layer. The film thickness thereof is about 10 to 50 nm.Subsequently, as shown in FIG. 3C, the semiconductor layer 220 ispatterned using typical photolithography and dry etching. As a result,the island-shaped semiconductor layer 220 is formed. Around thesemiconductor layer 220, the cap insulating layer 171 is exposed.

Next, as shown in FIG. 3D, over the semiconductor layer 220 and the capinsulating layer 171, an insulating film (hereinafter referred to alsoas the covering insulating film 226) serving as the sidewalls 226 isformed by, e.g., a CVD method. Examples of the covering insulating film226 (insulating film serving as the sidewalls 226) include silicondioxide (SiO₂) and silicon nitride (SiN). The film thickness thereof isabout 20 to 200 nm. The covering insulating film 226 covers not only thetop surfaces of the cap insulating layer 171 and the semiconductor layer220, but also the exposed side surfaces of the semiconductor layer 220.

Next, as shown in FIG. 3E, the covering insulating film 226 is subjectedto a full etch-back process. As a result, the covering insulating film226 is removed from the top surfaces of the cap insulating layer 171 andthe semiconductor layer 220, while the sidewalls 226 are formed over theside surfaces of the semiconductor layer 220. The sidewalls 226 coverand protect the exposed side surfaces of the island-shaped semiconductorlayer 220 such that the semiconductor layer 220 is not affected byanother film or process.

Next, as shown in FIG. 3F, over the top surfaces of the cap insulatinglayer 171, the sidewalls 226, and the semiconductor layer 220, the gateinsulating film 221 and the gate electrode 222 are deposited by, e.g., asputtering method. In this case, the gate insulating film 221 covers thesemiconductor layer 220 and the sidewalls 226. Here, the side surfacesof the semiconductor layer 220 are covered with the sidewalls 226 and donot show steep steps. Accordingly, the gate insulating film 221 isuninterruptedly continued from over the semiconductor layer 220 to thecap insulating layer 171. As a result, the side surfaces of the ends ofthe semiconductor layer 220 are protected not only with the sidewalls266, but also with the gate insulating film 221. This more reliablyprevents contact between the side surfaces of the ends of thesemiconductor layer 220 and the gate electrode 222.

Examples of the material of the gate insulating film 221 include siliconoxide (SiO₂), silicon nitride (SiN_(x)), and an oxide of a metal such asHf, Zr, Al, or Ta. Alternatively, a combination of the foregoingmaterials may also be used. The gate insulating film 221 made of such amaterial may also include nitrogen, carbon, or the like in addition to ametal and oxygen. The film thickness thereof is preferably about 0.5 to50 nm. Thus, the semiconductor element 200 is provided with thededicated gate insulating film 221. This allows a desired material to beused as the gate insulating film having a desired film thickness. As aresult, an increase in gate capacitance (i.e., a characteristicimprovement) and the like can be easily achieved.

On the other hand, examples of the material of the gate electrode 222include titanium (Ti), titanium nitride (TiN), aluminum (Al), cobalt(Co), molybdenum (Mo), tantalum (Ta), tantalum nitride (TaN), tungsten(W), and tungsten nitride (WN). Alternatively, any of the foregoingmaterials in which carbon (C) or oxygen (O) is mixed or a laminatedstructure of any of the foregoing materials and another metal or thelike may also be used. The film thickness thereof is preferably about 5to 100 nm. Thus, the semiconductor element 200 is provided with thededicated gate electrode 222. This allows a desired metal material to beused for the gate electrode. The material of the gate electrode 222determines the effective work function of the semiconductor element(in-wiring-layer active element (component)) 200. As a result, there isno limit to the work function of the gate electrode to allow thethreshold voltage to be set.

Next, as shown in FIG. 3G, using typical photolithography and dryetching, the gate electrode 222 and the gate insulating film 221 arepatterned. By the patterning, a gate electrode shape as shown in theplan view of FIG. 2 is defined. That is, the gate electrode 222 and thegate insulating film 221 are patterned into such a gate electrode shapeas to extend completely across (extend over) the semiconductor layer 220(including the sidewalls 226) (there is also a form in which the gateinsulating film 221 extends not completely across the semiconductorlayer 220). At this time, as described above, the side surfaces of theends of the semiconductor layer 220 are protected not only with thesidewalls 266, but also with the gate insulating film 221. This morereliably prevents contact between the side surfaces of the ends of thesemiconductor layer 220 and the gate electrode 222.

Next, as shown in FIG. 3H, the second interlayer insulating layer 172 isformed so as to cover the cap insulating layer 171, the sidewalls 226,the semiconductor layer 220, the gate insulating film 221, and the gateelectrode 222. The second interlayer insulating layer 172 is alow-dielectric-constant insulating layer having a dielectric constantlower than that of silicon dioxide. Examples of the material of thesecond interlayer insulating layer 172 include a carbon-containing filmsuch as a SiOC(H) film or SiLK (registered trademark). Subsequently, asshown in FIG. 3I, in the second interlayer insulating layer 172, holes401 to 404 for the vias, the contact, and the wires are opened.Thereafter, as shown in FIG. 3J, the via 189, the contacts (source/drainelectrodes) 286, the via 290 for the gate electrode, and the secondwires 188, 285, and 289 are embedded using a single damascene method ora dual damascene method. As a result, the second wiring layer 170 isformed. Examples of the material of the vias 189 and 290, the contacts286, and the second wires 188, 285, and 289 include copper (Cu) usingtantalum (Ta)/tantalum nitride (TaN) or titanium (Ti)/titanium nitride(TiN) as a barrier film. At this time, the source/drain electrodes(contacts 286) are provided over the channel (semiconductor layer 220)after the formation of the channel (semiconductor 220). This allows thecontact resistance between the channel and the source/drain electrode tobe sufficiently reduced.

By the foregoing steps, the semiconductor device 100 according to thepresent embodiment is manufactured.

In the present embodiment, as the material of the gate electrode of thesemiconductor element 200, not the same material as that of wiring, buta dedicated material can be used. This solves the problem that the workfunction of the gate electrode is fixed when the same material as thatof wiring is used and allows any work function to be selected for thegate electrode. As a result, the threshold voltage of the semiconductorelement 200 can be set to allow the in-wiring-layer active element(component) to be set in each of a normally-on mode and a normally-offmode.

Also, in the present embodiment, as the gate insulating film of thesemiconductor element 200, not the Cu diffusion preventing layer, but adedicated insulating film can be used. This solves the problem that,when the Cu diffusion preventing layer is used, the gate insulating filmis excessively thickened to also satisfy a Cu diffusion barrierfunction, and allows the thickness of the gate insulating film to be setirrelevantly to the Cu diffusion barrier function. As a result, itbecomes possible to further reduce the thickness of the gate insulatingfilm and significantly increase the gate capacitance.

Also in the present embodiment, over the side surfaces of the ends ofthe semiconductor element 200, the sidewalls 226 are provided. By thefunction of the sidewalls 226, the semiconductor layer 220 and the gateelectrode 222 can be electrically and physically isolated. This solvesthe problem that a short circuit occurs between the end surface of thesemiconductor layer 220 and the gate electrode 222, and allows asignificant improvement in the production yield of the device.

First Variation

FIG. 4 is a cross-sectional view showing a first variation of theconfiguration of the semiconductor device according to the presentembodiment. When compared with the case shown in FIG. 1A, the case shownin FIG. 4 is different therefrom in that a hard mask 224 is providedover the gate electrode 222. Hereinbelow, a description will be givenmainly of the difference therebetween.

In the present variation, the hard mask 224 is used for the processingof the gate electrode 222 and prevents direct contact between a resistand the gate electrode 222. Since the hard mask 224 is processed usingthe resist, ashing is performed, and then the gate electrode 222 isprocessed using the hard mask 224, the gate electrode is not exposedduring the ashing of the resist. Accordingly, it is possible to avoidmodification of the electrode such as the oxidation thereof.

To obtain such a configuration, in the step of FIG. 3F in the foregoingmanufacturing method of the semiconductor device shown in FIGS. 3A to3J, over the top surfaces of the cap insulating layer 171, the sidewalls226, and the semiconductor layer 220, not only the gate insulating film221 and the gate electrode 222, but also the hard mask 224 may furtherbe deposited appropriately by, e.g., a plasma CVD method. Examples ofthe material of the hard mask 224 include insulating films of silicondioxide (SiO₂), silicon oxycarbide (SiOC), carbon (C), silicon nitride(SiN), and the like and a combination thereof. The film thicknessthereof is preferably, e.g., about 30 to 200 nm.

In the case of the present modification also, the same effect asobtained in the case shown in FIGS. 1A, 1B, and 2 can be obtained.

In addition, by the effect of the hard mask 224, it is possible toexcellently provide contact with the gate electrode 222.

Second Modification

FIG. 5A is a cross-sectional view showing a second modification of theconfiguration of the semiconductor device according to the presentembodiment. When compared with the case shown in FIG. 4, the case shownin FIG. 5A is different therefrom in that sidewalls 225 are providedover the both side surfaces of a laminated structure of the gateinsulating film 221, the gate electrode 222, and the hard mask 224.Hereinbelow, a description will be given mainly of the differencetherebetween.

In the present variation, when the contacts (source/drain electrodes)286 are formed, the sidewalls 225 prevents contact between the contacts(source/drain electrodes) 286 and the gate electrode 222. That is, whenthe holes 402 and 403 for the contacts 286 are formed, even if the holes402 and 403 come excessively close to the gate electrode 222, contactwith the gate electrode 222 can be prevented. As a result, the contacts286 can be formed at proper positions.

To obtain such a structure, in the foregoing manufacturing method(method to which the alteration according to the first modificationdescribed above has been added) of the semiconductor device shown inFIGS. 3A to 3J, between the steps of FIGS. 3G and 3H, the followingsteps may be added appropriately. First, in the same manner as in thestep of FIG. 3D, an insulating film (hereinafter referred to also as acovering insulating film 225) serving as the sidewalls 225 is formed by,e.g., a CVD method so as to cover the cap insulating layer 171, thesidewalls 226, the semiconductor layer 220, the gate insulating film221, the gate electrode 222, and the hard mask 224. Examples of thematerial of the covering insulating film 225 (insulating film serving asthe sidewalls 225) include silicon dioxide (SiO₂) and silicon nitride(SiN). The thickness thereof is about 10 to 200 nm. Then, in the samemanner as in the step of FIG. 3E, the covering insulating film 225 issubjected to a full etch-back process. As a result, the coveringinsulating film 225 is removed from the top surfaces of the capinsulating layer 171, the sidewalls 226, and the semiconductor layer220, while the sidewalls 225 are formed over the both side surfaces ofthe hard mask 224, the gate electrode 222, and the gate insulating film221.

In the case shown in the present modification also, the same effects asobtained in the case shown in FIG. 4 can be obtained.

In addition, by the effect of the sidewalls 225, it is possible toprevent contact between the contacts (source/drain electrodes) 286 andthe gate electrode 222 and form the contacts 286 at proper positions.

Third Modification

FIG. 5B is a cross-sectional view showing a third modification of theconfiguration of the semiconductor device according to the presentembodiment. When compared with the case shown in FIG. 5A, the case shownin FIG. 5B is different therefrom in that the hard mask 224 is notprovided over the gate electrode 222. In a manner, the relationshipbetween FIGS. 5A and 5B is the same as the relationship between FIGS. 1Aand 4. In the case shown in FIG. 5B also, the same effects as achievedin the case shown in FIG. 5A (except for the effect of the hard mask224) can be achieved.

Second Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the second embodiment. FIG. 6A is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. FIG. 7 is a plan view showing anexample of the configuration of the semiconductor device according tothe present embodiment. Note that FIG. 6A is a cross section along theline A-A′ of FIG. 7. The semiconductor device of the present embodimentis different from the semiconductor device particularly in the secondmodification (FIG. 5A) of the first embodiment in that each of thecontacts (source/drain electrodes) 286 is provided in a self-alignedmanner. Hereinbelow, a description will be given mainly of thedifference therebetween.

In the present embodiment, over the both side surfaces of the laminatedstructure of the hard mask 224, the gate electrode 222, and the gateinsulating film 221, the sidewalls 225 are provided. The contacts(source/drain electrodes of the semiconductor element 200) 286 areprovided in such a manner as to come in contact with the sidewalls 225.The gate electrode 222 has a shape which extends across thesemiconductor layer 220 and the sidewalls 226. By the sidewalls 225, thepositions of the contacts 286 are defined, and therefore the contacts286 can be formed at proper positions.

In the semiconductor device according the present embodiment, asaccording to, e.g., the relationship between FIGS. 5A and 5B, the hardmask 224 need not be provided (or may be provided) over the gateelectrode 222. FIG. 6B is a cross-sectional view showing another exampleof the configuration of the semiconductor device according to thepresent embodiment. When compared with the case shown in FIG. 6A, thecase shown in FIG. 6B is different therefrom in that the hard mask 224is not provided over the gate electrode 222. In a manner, therelationship between FIGS. 6B and 6A is the same as the relationshipbetween FIGS. 5B and 5A. In the case shown in FIG. 6B also, the sameeffects (except for the effect of the hard mask 224) as shown in FIG. 6Acan be achieved.

Such a configuration as shown in FIG. 6A can be implemented by thefollowing steps. FIGS. 8A to 8E are cross-sectional views showing anexample of a manufacturing method of the semiconductor device accordingto the present embodiment. Each of the drawings corresponds to a crosssection along the line A-A′ of FIG. 7. Note that, in FIGS. 8A to 8E, theillustration of the semiconductor substrate 101, the contact layer 130,and the wiring layer 140 is omitted.

First, after the steps in the manufacturing method of the semiconductordevice of the first embodiment shown in FIGS. 3A to 3E, in the step ofFIG. 3F, not only the gate insulating film 221 and the gate electrode222, but also the hard mask 224 is further deposited by, e.g., a plasmaCVD method over the top surfaces of the cap insulating layer 171, thesidewalls 226, and the semiconductor layer 220. Examples of the materialof the hard mask 224 include insulating films of silicon dioxide (SiO₂),silicon oxycarbide (SiOC), carbon (C), silicon nitride (SiN), and thelike and a combination thereof. The film thickness thereof is preferablyabout 30 to 200 nm. Then, in the same manner as in the step shown inFIG. 3G, using typical photolithography and dry etching, the hard mask224, the gate electrode 222, and the gate insulating film 221 arepatterned. By the patterning, a gate electrode shape as shown in theplan view of FIG. 7 is defined. That is, the hard mask 224, the gateelectrode 222, and the gate insulating film 221 are patterned into thegate electrode shape which extends completely across (extends over) thesemiconductor layer 220 (including the sidewalls 226).

Next, as shown in FIG. 8A, the insulating film (hereinafter referred toalso as the covering insulating film 225) serving as the sidewalls 225is formed by, e.g., a CVD method so as to cover the cap insulating layer171, the sidewalls 226, the semiconductor layer 220, the gate insulatingfilm 221, the gate electrode 222, and the hard mask 224. Examples of thematerial of the covering insulating film 225 (insulating film serving asthe sidewalls 225) include silicon dioxide (SiO₂) and silicon nitride(SiN). The thickness thereof is about 10 to 200 nm.

Next, as shown in FIG. 8B, the covering insulating film 225 is subjectedto a full etch-back process. As a result, the covering insulating film225 is removed from the top surfaces of the cap insulating layer 171,the sidewalls 226, and the semiconductor layer 220, while the sidewalls225 are formed over the both side surfaces of the hard mask 224, thegate electrode 222, and the gate insulating film 221.

Next, as shown in FIG. 8C, the second interlayer insulating layer 172 isformed so as to cover the cap insulating layer 171, the sidewalls 226,the semiconductor layer 220, the sidewalls 225, the gate insulating film221, the gate electrode 222, and the hard mask 224. The secondinterlayer insulating layer 172 is a low-dielectric-constant layerhaving a dielectric constant lower than that of silicon dioxide.Examples of the material of the second interlayer insulating layer 172include a carbon-containing film such as a SiOC(H) film or SiLK(registered trademark). Subsequently, as shown in FIG. 8D, in the secondinterlayer insulating layer 172, the holes 401 to 404 for the vias, thecontacts, and the wires are opened. In this case, the holes 402 and 403for the contacts (source/drain electrodes) 286 are disposed closer tothe sidewalls 225 than in the second modification (FIG. 5A) of the firstembodiment. In addition, the etching rate of the material of thesidewalls 225 is significantly lower than the etching rate of thematerial of the second interlayer insulating layer 172. In other words,each of the holes 402 and 403 has a part thereof corresponding to thesidewall 225, and therefore the sidewall 225 may be etched together withthe second interlayer insulating layer 172 during etching. However,since the etching rate of the sidewalls 225 is significantly low, onlythe second interlayer insulating layer 172 is etched, and the holes 402and 403 can be formed in a so-called self-aligned manner with respect tothe gate electrode 222.

Next, as shown in FIG. 8E, the via 189, the contacts (source/drainelectrodes) 286, the via 290 for the gate electrode, and the secondwires 188, 285, and 289 are embedded using a single damascene method ora dual damascene method. In this manner, the second wiring layer 170 isformed. Examples of the via 189, the contacts 186 and 290, and thesecond wires 188, 285, and 289 include copper (Cu) using tantalum(Ta)/tantalum nitride (TaN) or titanium (Ti)/titanium nitride (TiN) as abarrier film. In this case, since the contacts (source/drain electrodes)286 are disposed in a so-called self-aligned manner with respect to thegate electrode 222, the contacts 286 can be formed at proper positions.

By the foregoing steps, the semiconductor device 100 according to thepresent embodiment is manufactured.

However, to enable the foregoing semiconductor element 200 to be placed,it is necessary to carefully select a material for the hard mask 224 andthe sidewalls 225. As the material of the hard mask 224 and thesidewalls 225, a material having a selectivity different from that ofthe second interlayer insulating layer 172 is preferably selected. Forexample, when silicon dioxide (SiO₂) is used as the material of thesecond interlayer insulating layer 172, it can be considered to usesilicon nitride (SiN_(x)) or the like as the material of the hard mask224 and the sidewalls 225. As a result, when the holes 402 and 403 forthe contacts 286 are opened, it is possible to selectively leave thesidewalls 225 and prevent the gate electrode 222 from being exposedduring the etching for opening the holes 402 and 403.

In the present embodiment also, the same effects as obtained in thefirst embodiment can be obtained.

In addition, in the present embodiment, the semiconductor element 200has a top-gate element structure, not a bottom-gate element structure,and can be placed in a self-aligned manner. Accordingly, it is possibleto precisely control the distances between the source/drain electrodes(contacts 286) and the gate (gate insulating film 221 and gate electrode222). That is, alignment accuracy can be improved. When silicon nitride(SiN_(x)) or the like is used for the sidewalls 225 and the hard mask224, the etching resistance thereof can prevent a short circuit betweenthe gate and the source/drain electrodes.

Modification

FIG. 9 is a cross-sectional view showing a modification of theconfiguration of the semiconductor device according to the presentembodiment. When compared to the case shown in FIG. 6A, the case shownin FIG. 9 is different therefrom in that the drain electrode (contact286 (D)) is formed at a position distant from the sidewall 225.Hereinbelow, a description will be given mainly of the differencetherebetween.

In the present embodiment, of the contacts 286 as the source/drainelectrodes, the contact 286 (D) as the drain electrode is formed at aposition distant from the sidewall 225. The placement is determined bylithography. On the other hand, the contact 286 (S) as the sourceelectrode is formed at a position in contact with the sidewall 225, inthe same manner as in the case shown in FIG. 6A.

Such a configuration can be implemented by adjusting the position of thehole 403 for the contact (source/drain electrode) 286 in the step ofFIG. 8D in the manufacturing method of the semiconductor deviceaccording to the second embodiment described above. It is also possibleto further provide sidewalls outside the sidewall 225 closer to thecontact 286 (D) to provide the double sidewalls and thereby produce theshape of FIG. 9 by self alignment.

In the present modification also, the same effects as obtained in thesecond embodiment can be obtained.

In addition, in the present modification, by physically isolating thedrain electrode (contact 286 (D)) from the gate electrode 222, the drainbreakdown voltage of the semiconductor element 200 can be improved. Onthe other hand, by forming the source electrode (contact 286 (S)) byself alignment, the distance between the source electrode (contact 286(S)) and the gate (gate insulating film 221 and gate electrode 222) canbe precisely controlled with the width of the sidewall 225. This allowsthe source-side parasitic resistance to be minimized.

Third Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the third embodiment. FIG. 10 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. The semiconductor device of thepresent embodiment is different from the semiconductor device of thesecond embodiment in having a double-gate structure including a backgate 210. Hereinbelow, a description will be given mainly of thedifference therebetween.

In the present embodiment, the back gate 210 is provided in the surfaceregion of the first wiring layer 150, similarly to the first wire (Cuwire) 164 in the first wiring layer 150. The back gate 210 has the topsurface thereof covered with the cap insulating layer 171. The back gate210 is provided at a position opposing the gate electrode 222 via thecap insulating layer 171 and the semiconductor layer 220. For example,the back gate 210 is provided so as to cover the region of thesemiconductor layer 220 extending from one (source electrode) of thecontacts 286 to the other contact (drain electrode) 286 through the gateelectrode 222. That is, the semiconductor layer 220 has the double gatestructure having the gate electrode 222 and the back gate 210.

However, it is also possible to apply the back gate 210 provided in thepresent embodiment to each of the semiconductor elements 200 of thefirst embodiment, the modifications thereof, and the modification of thesecond embodiment.

To obtain such a configuration, when the first wiring layer 150 isformed in the manufacturing method of the semiconductor device of thesecond embodiment (in the step of FIG. 3A), the back gate (Cu wire) 210is formed simultaneously with the first wire (Cu wire) 164. This allowsthe back gate 210 to be formed without providing an additional step.Moreover, when the gate electrode 222 and the like are formed, since thesemiconductor layer 220 is formed over the region where the back gate210 exists, the gate electrode 222 and the like are aligned with respectto the back gate 210 and patterned.

In the present embodiment also, the same effects as obtained in thesecond embodiment can be obtained.

In addition, in the present embodiment, the semiconductor element 200 isformed in the double gate structure to allow switching between thesource/drain electrodes to be performed with a more excellent ON/OFFratio. In addition, the sub-threshold characteristic is improved toallow driving at a lower voltage.

Modification

FIG. 11 is a cross-sectional view showing a modification of theconfiguration of the semiconductor device according to the presentembodiment. Compared with the case shown in FIG. 10, the case shown inFIG. 11 is different therefrom in that the back gate 210 is disposed inthe limited region of the semiconductor layer 220. Hereinbelow, adescription will be given mainly of the difference therebetween.

In the present modification, the back gate 210 is provided at a positionopposing one (source electrode) of the contacts 286 and a part of thegate electrode 222 via the cap insulating layer 171 and thesemiconductor layer 220. Specifically, the back gate 210 is provided soas to cover the region of the semiconductor layer 220 extending from theone contact (source electrode) 286 to the gate electrode 222. Thus, inthe present embodiment, the back gate 210 is disposed in the limitedregion of the channel (semiconductor layer 220).

Such a configuration can be implemented by, e.g., displacing theposition of the back gate (Cu wire) 210 when the back gate (Cu wire) 210is formed in the first wiring layer 150 in the manufacturing method ofthe semiconductor device of the third embodiment. Alternatively, whenthe gate electrode 222 and the like are formed, the gate electrode 222and the like are aligned to be slightly displaced from the back gate 210and patterned to allow such a configuration to be implemented.

In the present modification also, the same effects as obtained in thethird embodiment can be obtained.

In addition, in the present modification, it is possible to cause thedouble-gate effect due to the back gate 210 only between, e.g., thesource (the one contact 286) and the gate (gate electrode 222).Consequently, even when, e.g., the sidewalls 225 are thickened, aparasitic resistance can be sufficiently reduced by the back gate 210between the source and gate while, between the source and the drain, thedrain breakdown voltage can be precisely determined with the distancedefined by the film thickness of the sidewall 225. That is, by thuschanging the position of the back gate 210 to a desired position, theelement characteristics of the semiconductor element 200 can beoptimized.

Fourth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the fourth embodiment. FIG. 1s a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. FIG. 13 is a plan view showing theexample of the configuration of the semiconductor device according tothe present embodiment. Note that FIG. 12 is a cross section along theline A-A′ of FIG. 13. The semiconductor device of the present embodimentis different from the semiconductor device of the first embodiment (FIG.1A) in that the gate insulating film 221 covers the entire upper surfaceof the semiconductor layer 220. Hereinbelow, a description will be givenmainly of the difference therebetween.

In the present embodiment, the gate insulating film 221 covers theentire upper surface of the island-shaped semiconductor layer 220. Thatis, the gate insulating film 221 overlaps the semiconductor layer 220 inplanar view. In addition, the sidewalls 226 cover the both side surfacesof the semiconductor layer 220 and the gate insulating film 221. Notethat the present embodiment also includes a form in which the gateinsulating film 221 in the region where the gate electrode 222 does notexist is thinner than the gate insulating film 221 immediately under thegate electrode 222 or is partly missing. In this case, as will bedescribed later, patterning is performed after the gate insulating film221 is formed over the semiconductor layer 220. As a result, thesemiconductor layer 220 is no longer affected by the patterning to alloweasy control of the film quality thereof. In addition, contact betweenthe gate electrode 222 and the semiconductor layer 220 can be morereliably prevented.

Such a configuration can be implemented by the following steps. FIGS.14A to 14J are cross-sectional views each showing an example of amanufacturing method of the semiconductor device according to thepresent embodiment. Each of the drawings corresponds to a cross sectionalong the line A-A′ of FIG. 13. Note that, in FIGS. 14A to 14J, theillustration of the semiconductor substrate 101, the contact layer 130,and the wiring layer 140 is omitted.

First, as shown in FIG. 1B, the semiconductor substrate 101 is formedwith the isolating layer 120. Then, over the semiconductor substrate101, e.g., the transistor 121 is formed as the semiconductor element.Subsequently, the contact layer 130 (including the interlayer insulatinglayer 131 and the contacts 142), and the wiring layer 140 (including theinterlayer insulating layer 132 and the wires (copper (Cu) wires) 144)are formed. For the foregoing steps, a conventionally known method canbe used.

Next, as shown in FIG. 14A, over the wiring layer 140 (not shown), thecap insulating layer 151 for preventing diffusion of copper (Cu) and thefirst interlayer insulating layer 152 are deposited in this order.Subsequently, in the first interlayer insulating layer 152, the via 162and the first wire 164 are embedded using a single damascene method or adual damascene method. In this manner, the first wiring layer 150 isformed. Thereafter, the cap insulating layer 171 is formed so as tocover the first interlayer insulating film 152 and the first wire 164.The foregoing steps are performed by the same method as used to form atypical semiconductor device having a copper (Cu) wiring layer.

Next, as shown in FIG. 14B, over the cap insulating layer 171, thesemiconductor layer 220 serving as the channel of the semiconductorelement 200 is formed by, e.g., a sputtering method. Further, the gateinsulating film 221 is deposited thereover by, e.g., a sputteringmethod. Subsequently, as shown in FIG. 14C, the gate insulating film 221is patterned by typical photolithography and dry etching. As a result,the island-shaped gate insulating film 221 is formed. Then, as shown inFIG. 14D, the semiconductor layer 220 under the gate insulating film 221is patterned by dry etching using the gate insulating film 221 as amask. As a result, a laminated structure of the island-shaped gateinsulating film 221 and the semiconductor layer 220 is formed.

Next, as shown in FIG. 14E, over the gate insulating film 221 and thecap insulating layer 171, an insulating film (hereinafter referred toalso as the covering insulating film 226) serving as the sidewalls 226is formed by, e.g., a CVD method. Then, the covering insulating film 226is subjected to a full etch-back process. As a result, over the sidesurfaces of the gate insulating film 221 and the semiconductor layer220, the sidewalls 226 are formed. The sidewalls 226 cover and protectthe exposed side surfaces of the island-shaped semiconductor layer 220such that the semiconductor layer 220 is not affected by another film orprocess.

Next, as shown in FIG. 14F, over the top surfaces of the cap insulatinglayer 171, the sidewalls 226, and the gate insulating film 221, the gateelectrode 222 and the hard mask 224 are deposited by, e.g., a sputteringmethod. Subsequently, as shown in FIG. 14G, using typicalphotolithography and dry etching, the hard mask 224 is patterned.Subsequently, as shown in FIG. 14H, the gate electrode 222 under thehard mask 224 is patterned by dry etching using the hard mask 224 as amask. As a result, a laminated structure of the hard mask 224 and thegate electrode 222 which has a gate electrode shape as shown in the planview of FIG. 13 is formed.

Next, as shown in FIG. 14I, the second interlayer insulating layer 172is formed so as to cover the cap insulating layer 171, the sidewalls226, the gate insulating film 221, the gate electrode 222, and the hardmask 224. Subsequently, as shown in FIG. 14J, in the second interlayerinsulating layer 172, the holes for the vias, the contacts, and thewires are opened. Thereafter, the via 189, the contacts (source/drainelectrodes) 286, the via 290 for the gate electrode, and the secondwires 188, 285, and 289 are embedded using a single damascene method ora dual damascene method. As a result, the second wiring layer 170 isformed.

By the foregoing steps, the semiconductor device 100 according to thepresent embodiment is manufactured.

Note that, as a method for forming the sidewalls 226, a technique whichoxidizes the end surfaces of the semiconductor layer 220 to partiallychange the semiconductor layer 220 into an insulator or the like canalso be used besides the step of FIG. 14E described above. Note that,when the gate electrode 222 is patterned, the gate insulating film 221is also etched. Therefore, the present embodiment also includes a formin which the gate insulating film 221 in the region where the gateelectrode 222 does not exist is thinner than the gate insulating film221 immediately under the gate 222 or is missing.

In the present embodiment also, the same effects as obtained in thefirst embodiment can be obtained.

In addition, in the present embodiment, patterning is performed afterthe gate insulating film 221 is formed over the semiconductor layer 220so that the semiconductor layer 220 is no longer affected by thepatterning (no longer affected by direct application of a resist and aresist removing operation). This allows easy control of the film qualityof the semiconductor layer 220, specifically control of a compositionsuch as oxygen in the semiconductor layer 220 and the like.

Fifth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to a fifth embodiment. FIG. 15 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. FIG. 16 is plan view showing theexample of the configuration of the semiconductor device according tothe present embodiment. Note that FIG. 15 is a cross section along theline A-A′ of FIG. 16. The semiconductor device of the present embodimentis different from the semiconductor device of the fourth embodiment(FIG. 12) in that the gate electrode includes two layers. Hereinbelow, adescription will be given mainly of the difference therebetween.

In the present embodiment, the gate electrode includes the two layers ofthe lower gate electrode 222 and an upper gate electrode 223. The lowergate electrode 222 exists only over the semiconductor layer 220. Theupper gate electrode 223 is formed not only to exist over thesemiconductor layer 200, but also to extend across the semiconductorlayer 220. The materials of the two gate electrodes may be the same asor different from each other. Note that the present embodiment alsoincludes a form in which the gate insulating film 221 in the regionwhere the lower gate electrode 222 does not exist is thinner than thegate insulating film 221 immediately under the lower gate electrode 222or is missing. In this case, as will be described later, patterning isperformed after the gate insulating film 221 and the lower gateelectrode 222 are formed over the semiconductor layer 220. As a result,the semiconductor layer 220 and the gate insulating film 221 are nolonger affected by the patterning to allow easy control of the filmquality thereof.

Such a configuration can be implemented by the following steps. FIGS.17A to 17H are cross-sectional views showing an example of amanufacturing method of the semiconductor device according to thepresent embodiment. Each of the drawings corresponds to a cross sectionalong the line A-A′ of FIG. 16. Note that, in FIGS. 17A to 17H, theillustration of the semiconductor substrate 101, the contact layer 130,and the wiring layer 140 is omitted.

First, as shown in FIG. 1B, the semiconductor substrate 101 is formedwith the isolating layer 120. Then, over the semiconductor substrate101, e.g., the transistor 121 is formed as the semiconductor element.Subsequently, the contact layer 130 (including the interlayer insulatinglayer 131 and the contacts 142), and the wiring layer 140 (including theinterlayer insulating layer 132 and the wires (copper (Cu) wires) 144)are formed. For the foregoing steps, a conventionally known method canbe used.

Next, as shown in FIG. 17A, over the wiring layer 140 (not shown), thecap insulating layer 151 for preventing diffusion of copper (Cu) and thefirst interlayer insulating layer 152 are deposited in this order.Subsequently, in the first interlayer insulating layer 152, the via 162and the first wire 164 are embedded using a single damascene method or adual damascene method. In this manner, the first wiring layer 150 isformed. Thereafter, the cap insulating layer 171 is formed so as tocover the first interlayer insulating film 152 and the first wire 164.The foregoing steps are performed by the same method as used to form atypical semiconductor device having a copper (Cu) wiring layer.

Next, as shown in FIG. 17B, over the cap insulating layer 171, thesemiconductor layer 220 serving as the channel of the semiconductorelement 200, the gate insulating film 221, and the lower gate electrode222 are deposited in this order by, e.g., a sputtering method.Subsequently, as shown in FIG. 17C, the lower gate electrode 222 ispatterned by typical photolithography and dry etching. As a result, theisland-shaped lower gate electrode 222 is formed. Then, as shown in FIG.17D, the gate insulating film 221 and the semiconductor layer 220 eachunder the lower gate electrode 222 are patterned by dry etching usingthe lower gate electrode 222 as a mask. As a result, a laminatedstructure of the island-shaped lower gate electrode 222, the gateinsulating film 221, and the semiconductor layer 220 is formed. At thistime, the gate insulating film 221 and the semiconductor layer 220 areprotected by the lower gate electrode 222 and therefore scarcelyaffected by photolithography and dry etching.

Next, as shown in FIG. 17E, over the lower gate electrode 222 and thecap insulating layer 171, an insulating film (hereinafter referred toalso as the covering insulating film 226) serving as the sidewalls 226is formed by, e.g., a CVD method. Then, the covering insulating film 226is subjected to a full etch-back process. As a result, over the sidesurfaces of the lower gate electrode 222, the gate insulating film 221,and the semiconductor layer 220, the sidewalls 226 are formed. Thesidewalls 226 cover and protect the exposed side surfaces of theisland-shaped gate insulating film 221 and the semiconductor layer 220such that the gate insulating film 221 and the semiconductor layer 220are not affected by another film or process.

Next, as shown in FIG. 17F, over the top surfaces of the cap insulatinglayer 171, the sidewalls 226, and the lower gate electrode 222, theupper gate electrode 223 and the hard mask 224 are deposited by, e.g., asputtering method. Subsequently, as shown in FIG. 17G, using typicalphotolithography and dry etching, the hard mask 224 is patterned.Subsequently, as shown in FIG. 17H, the upper gate electrode 222 and thelower gate electrode 222 each under the hard mask 224 are patterned bydry etching using the hard mask 224 as a mask. As a result, a laminatedstructure of the hard mask 224, the upper gate electrode 223, and thelower gate electrode 222 which has a gate electrode shape as shown inthe plan view of FIG. 16 is formed. Note that, since the gate insulatingfilm 221 is also etched when the lower gate electrode 222 is patterned,the present embodiment also includes a form in which the gate insulatingfilm 221 in the region where the lower gate electrode 222 does not existis thinner than the gate insulating film 221 immediately under the lowergate electrode 222 or missing.

The subsequent steps are as shown in the steps of FIGS. 14I to 14J inthe manufacturing method of the semiconductor device according to thefourth embodiment.

By the foregoing steps, the semiconductor device 100 according to thepresent embodiment is manufactured.

In the present embodiment also, the same effects as obtained in thefourth embodiment can be obtained.

In addition, in the present embodiment, the lower gate electrode 222 isformed over the semiconductor layer 220 and the gate insulating film 221and then patterned into the channel shape. Thereafter, the upper gateelectrode 223 is formed and then patterned into the gate electrodeshape. As a result, the semiconductor layer 220 and the gate insulatingfilm 221 are no longer affected by the patterning (no longer affected bydirect application of a resist and a resist removing operation). Thisallows easy control of the film quality of each of the semiconductorlayer 220 and the gate insulating film 221 (specifically, control of acomposition such as oxygen in the semiconductor layer 220, damage in thegate insulating film, oxygen loss, and the like).

Sixth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to a sixth embodiment. FIG. 18 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. FIG. 19 is plan view showing anexample of the configuration of the semiconductor device according tothe present embodiment. Note that FIG. 18 is a cross section along theline A-A′ of FIG. 19. The semiconductor device of the present embodimentis different from the semiconductor device of the fourth embodiment(FIG. 12) in that the gate insulating film has a double structure.Hereinbelow, a description will be given mainly of the differencetherebetween.

In the present embodiment, over the gate insulating film 221, a gateinsulating film is further formed. The gate insulating film is thecovering insulating film 226 for the sidewalls 226 which is left as isover the gate insulating film 221 without being etched back (hereinafterreferred to as the second gate insulating film 226). Accordingly, thesecond gate insulating film 226 covers the upper and end surfaces of thelaminated structure of the semiconductor layer 220 and the gateinsulating film 221 that have been patterned. That is, over theprocessed side surfaces of the semiconductor layer 220, the second gateinsulating film 226 is formed as the sidewalls.

Such a configuration can be implemented by not performing a fulletch-back process on the covering insulating film 226 in the step ofFIG. 14E in the manufacturing method of the semiconductor deviceaccording to the fourth embodiment. In this case, the materials andthicknesses of the gate insulating film 221 and the covering insulatingfilm 226 are set in consideration of the laminated structure of the gateinsulating film. Note that the present embodiment also includes a formin which the gate insulating film 221 in the region where the gateelectrode 222 does not exist is thinner than the gate insulating film221 immediately under the lower gate electrode 222 or missing.

In the present modification also, the same effects as obtained in thefourth embodiment can be obtained.

In addition, in the present embodiment, the step of etching back thecovering insulating film 226 is no longer necessary to allow themanufacturing process to be simplified. Moreover, since the step ofetching back the covering insulating film 226 is not performed, damageto the gate insulating film and the like can be reduced. Depending onthe material, a strain can also be introduced into the semiconductorlayer 220 (channel) to allow an improvement in carrier mobility in thesemiconductor layer 220.

Seventh Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to a seventh embodiment. FIG. 20 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. The semiconductor device of thepresent embodiment is different from the semiconductor device of thefirst embodiment (FIG. 1A) in which the semiconductor element(in-wiring-layer active element (component)) 200 is formed in the copper(Cu) wiring layer in that the semiconductor element (in-wiring-layeractive element (component)) 200 is formed in an aluminum (Al) wiringlayer. Hereinbelow, a description will be given mainly of the differencetherebetween.

In the present embodiment, the semiconductor element (in-wiring-layeractive element (component)) 200 is formed in the aluminum (Al) wiringlayer. That is, the first wiring layer 150 includes the first wire 166and the via 168 each made of aluminum (Al), and the second wiring layer170 includes the second wire 186 and the via 189 each made of aluminum(Al). The semiconductor element 200 is formed in the second wiringlayer, but the element structure thereof is the same as in the caseshown in FIG. 1A.

Next, a description will be given of a manufacturing method of thesemiconductor device according to the present embodiment. FIGS. 21A to21G are cross-sectional views showing an example of the manufacturingmethod of the semiconductor device according to the present embodiment.Note that, in FIGS. 21A to 21G, the illustration of the semiconductorsubstrate 101, the contact layer 130, and the wiring layer 140 isomitted.

First, as shown in FIG. 1B, the semiconductor substrate 101 is formedwith the isolating layer 120. Then, over the semiconductor substrate101, e.g., the transistor 121 is formed as the semiconductor element.Subsequently, the contact layer 130 (including the interlayer insulatinglayer 131 and the contacts 142), and the wiring layer 140 (including theinterlayer insulating layer 132 and the wire (aluminum (Al) wire) 144)are formed. For the foregoing steps, a conventionally known method canbe used.

Next, as shown in FIG. 21A, after the first wire 166 of aluminum (Al) isformed, the first interlayer insulating layer 152 is deposited.Subsequently, in the first interlayer insulating layer 152, the via 168is embedded using a damascene method. In this manner, the first wiringlayer 150 is formed. The foregoing steps are performed by the samemethod as used to form a typical semiconductor device having an aluminum(Al) wiring layer.

Next, as shown in FIG. 21B, over the first interlayer insulating layer152, the second wire 186 of aluminum (Al) is formed. Subsequently, asshown in FIG. 21C, over the second wire 186 and the first interlayerinsulating layer 152, the semiconductor layer 220 serving as the channelof the semiconductor element 200 is formed by, e.g., a sputteringmethod. Then, the semiconductor layer 220 is patterned using typicalphotolithography and dry etching. As a result, the island-shapedsemiconductor layer 220 is formed.

Next, as shown in FIG. 21D, over the semiconductor layer 220, the secondwire 186, and the first interlayer insulating layer 152, an insulatingfilm (hereinafter referred to also as the covering insulating film 226)serving as the sidewalls 226 is formed by, e.g., a CVD method. Then, thecovering insulating film 226 is subjected to a full etch-back process.As a result, over the side surfaces of the semiconductor layer 220, thesidewalls 226 are formed. The sidewalls 226 cover and protect theexposed side surfaces of the island-shaped semiconductor layer 220 suchthat the semiconductor layer 220 is not affected by another film orprocess.

Next, as shown in FIG. 21E, over the top surfaces of the sidewalls 226,the semiconductor layer 220, the second wire 186, and the firstinterlayer insulating layer 152, the gate insulating film 221 and thegate electrode 222 are deposited by, e.g., a sputtering method. Then,using typical photolithography and dry etching, the gate electrode 222and the gate insulating film 221 are patterned. In this manner, the gateelectrode 222 and the gate insulating film 221 are patterned into a gateelectrode shape which extends completely across (extends over) thesemiconductor layer 220 (including the sidewalls 226). At this time, theside surfaces of the ends of the semiconductor layer 220 are protectednot only by the sidewalls 226, but also by the gate insulating film 221.This more reliably prevents contact between the side surfaces of theends of the semiconductor layer 220 and the gate electrode 222.

Next, as shown in FIG. 21F, the second interlayer insulating layer 172is formed so as to cover the sidewalls 226, the semiconductor layer 220,the gate electrode 222, the second wire 186, and the first interlayerinsulating layer 152. Subsequently, as shown in FIG. 21G, in the secondinterlayer insulating layer 172, the holes for the vias and the contactsare opened. Then, the via 189, the contacts (source/drain electrodes)286, and the via 290 for the gate electrode are embedded using adamascene method. As a result, the second wiring layer 170 is formed.

By the foregoing steps, the semiconductor device 100 according to thepresent embodiment is manufactured.

In the present embodiment also, irrespective of the type of the wiringlayer, the same effects as obtained in the first embodiment can beobtained. That is, irrespective of the generation of the semiconductordevice, the semiconductor element (in-wiring-layer active element(component)) 200 can be incorporated in the wiring layer.

Eighth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to an eighth embodiment. FIG. 22 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. The semiconductor device of thepresent embodiment is different from the semiconductor device of theseventh embodiment (FIG. 20) in having a double gate structure having aback gate 211. Hereinbelow, a description will be given mainly of thedifference therebetween.

In the present embodiment, the semiconductor element 200 furtherincludes a back-gate insulating film 212 in contact with the lowerportion of the semiconductor layer 220, and the back gate 211 in contactwith the lower portion of the back-gate insulating film 212. Theback-gate insulating film 212 and the back gate 211 have the same shapeas that of the semiconductor layer 220 in planar view. The sidewalls 226cover the side surfaces of the semiconductor layer 220, the back-gateinsulating film 212, and the back gate 211. The first wiring layer 150includes a first wire (210) for the back gate 211, and a via 268coupling the first wire (210) to the back gate 211.

Such a configuration can be implemented by the following steps. First,in the step of FIG. 21A in the manufacturing method of the semiconductordevice according to the seventh embodiment, the first wire (210) isformed in addition to the first wire 166. Thereafter, the firstinterlayer insulating layer 152 is deposited. Then, in the firstinterlayer insulating layer 152, the via 268 is embedded in addition tothe via 168 using a damascene method. Subsequently, after the step ofFIG. 21B, in the step of FIG. 21C, over the second wire 186, the via268, and the first interlayer insulating layer 152, not thesemiconductor layer 220, but the back gate 211 is formed by, e.g., asputtering method, the back-gate insulating film 212 is formed by, e.g.,a DVD method, and the semiconductor layer 220 is formed by, e.g., asputtering method. Then, the laminated film of the back gate 211, theback-gate insulating film 212, and the semiconductor layer 220 ispatterned into an island shape using typical photolithography and dryetching. The subsequent steps are the same as the steps of FIGS. 21D to21G.

In the present embodiment also, the same effects as obtained in theseventh embodiment can be obtained.

In addition, according to the present embodiment, it is also possible toform a double gate structure in the aluminum (Al) wiring layer. Thisallows the semiconductor element (in-wiring-layer active element(component)) having the double gate structure to be incorporated in thewiring layer irrespective of the generation of the semiconductor device.

Ninth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the ninth embodiment. FIG. 23 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. FIG. 24 is a plan view showing anexample of the configuration of the semiconductor device according tothe present embodiment. Note that FIG. 23 is a cross section along theline A-A′ of FIG. 24. The semiconductor device of the present embodimentis different from the semiconductor device of the first embodiment (FIG.1A) in having a double gate structure having a charge retaining(storing) function. Hereinbelow, a description will be given mainly ofthe difference therebetween.

In the present embodiment, the semiconductor element 200 furtherincludes the insulating film 212, the cap insulating layer 171, and theback gate 210 which are provided under the semiconductor layer 220 inaddition to the gate insulating film 221 and the gate electrode 222which are provided over the semiconductor layer 220.

The back gate 210 is provided in the surface region of the first wiringlayer 150, similarly to the first wire (Cu wire) 164 in the first wiringlayer 150. The back gate 210 has the top surface thereof covered withthe cap insulating layer 171. The back gate 210 is provided at aposition opposing the gate electrode 222 via the cap insulating layer171 and the semiconductor layer 220. For example, the back gate 210 isprovided so as to cover the region extending from one (source electrode)of the contacts 286 of the semiconductor layer 220 to the other contact(drain electrode) 286 through the gate electrode 222. That is, thesemiconductor element 200 has the double gate structure having the gateelectrode 222 and the back gate 210.

In the cap insulating layer 171, charges extracted from thesemiconductor layer 220 by the voltage applied to the back gate 210 areretained or released therefrom into the semiconductor layer 220. Thus,the cap insulating layer 171 has the function of a charge retaininglayer. That is, the semiconductor element 200 has a memory function.Note that examples of the material of the cap insulating layer 171include silicon nitride (SiN_(x)) and silicon carbonitride (SiCN), andthe film thickness of the cap insulating layer 171 is about 10 to 50 nm.The insulating film 212 (tunnel insulating film) provides isolationbetween the cap insulating layer 171 and the semiconductor layer 220 soas to prevent inappropriate movement of charges. Examples of thematerial of the insulating film 212 include silicon dioxide (SiO₂),aluminum oxide (Al₂O₃), another metal oxide, and a combination thereof.The thickness of the insulating film 212 is about 3 to 20 nm.

Note that the cap insulating layer 171 located under the insulating film212 functions as the charge retaining layer.

However, a structure in which a new charge retaining film is interposedbetween the cap insulating layer 171 and the insulating film 212 mayalso be used. In this case, examples of the material of the interposedcharge retaining film include films of silicon nitride (SiN_(x)),silicon carbonitride (SiCN), aluminum oxide (Al₂O₃), and silicon dioxide(SiO₂) to each of which an extremely small amount of impurity has beenadded, another trap insulating film, a polysilicon floating gate,silicon nanocrystal embedded in a silicon dioxide film, and a metaloxide semiconductor. The thickness of the interposed charge retainingfilm is about 2 to 30 nm.

By having a structure described above, the semiconductor element 200according to the present embodiment can operate as, e.g., a memory.

The following is the operation of the semiconductor element 200 as thememory.

Data writing is implemented by, e.g., applying a predetermined voltage(e.g., +3 V or 0 V) to the back gate 210 and to the gate electrode 222to extract charges (e.g., electrons) from the semiconductor layer 220and injecting the charges into the cap insulating layer 171 as thecharge retaining layer. Data erasing is implemented by, e.g., applying apredetermined voltage (e.g., −3 V or +3 V) to the back gate 210 and tothe gate electrode 222 to eject charges (e.g., electrons) from the capinsulating layer 171 as the charge retaining layer and injecting thecharges into the semiconductor layer 220. Data reading is performed bydetecting a variation in the threshold voltage of a transistor(hereinafter referred to also as an upper transistor) including thesemiconductor layer 220, the gate insulating film 221, and the gateelectrode 222 since the threshold voltage varies in accordance with thequantity of the charges retained in the cap insulating layer 171. Morespecifically, the variation in threshold voltage is detected as avariation in the current value of the transistor at a given fixed readvoltage (voltage applied to the gate during reading). Accordingly, theback gate 210 can also be regarded as a control gate (or a controlelectrode) which controls the entrance/exit of charges. The gateelectrode 222 can also be regarded as a read gate (or a read gateelectrode) which performs data reading.

Also, the semiconductor element 200 according to the present embodimentcan operate as, e.g., a transistor having a controllable thresholdvoltage.

The following is the operation of the semiconductor element 200 as thetransistor having the controllable threshold voltage.

For example, by applying a predetermined voltage to the back gate 210and to the gate electrode 222 to extract charges from the semiconductorlayer 220 and injecting the charges into the cap insulating layer 171 asthe charge retaining layer, the threshold voltage of the uppertransistor described above can be changed. For example, when the uppertransistor is of an n-type, as the quantity of retained electrons as thecharges increases in the cap insulating layer 171, the threshold voltageincreases. On the other hand, when the upper transistor is of a p-type,as the quantity of retained holes as the charges increases in the capinsulating layer 171, the threshold voltage increases. At this time,through such retention of carriers by the cap insulating layer 171, thethreshold voltage can be permanently changed.

In addition, by controlling the voltage applied to the back gate 210 incorrespondence to the timing of the operation of the upper transistordescribed above, it is also possible to dynamically change the thresholdvoltage of the upper transistor.

Such a configuration can be produced by adding the followingmodifications to the manufacturing method of the semiconductor device ofthe first embodiment. First, when the first wiring layer 150 is formedin the step of FIG. 3A, the back gate (Cu wire) 210 is formedsimultaneously with the formation of the first wire (Cu wire) 164. Also,in the step of FIG. 3B, before the semiconductor layer 220 is formed,the insulating film 212 is formed over the cap insulating layer 171 by,e.g., a CVD method. Then, when the gate electrode 222 and the like areformed in the step of FIG. 3G, since the semiconductor layer 220 isformed over the region where the back gate 210 exists, the gateelectrode 222 and the like are aligned with respect to the back gate 210and patterned.

In the present embodiment also, the same effects as obtained in thefirst embodiment can be obtained.

In addition, in the present embodiment, it is possible to form the filmfor the charge retaining layer without adding a new step and interposethe tunnel insulating film between the charge retaining film and thechannel by adding only one depositing step. This allows the back gate210, the cap insulating layer 171, the insulating film 212, and thesemiconductor layer 220 to form a structure equivalent to an NMOS(Metal-Nitride-Oxide-Semiconductor) structure. As a result, thesemiconductor element 200 having a memory structure can be formed at lowcost. Additionally, the charge retaining function of the cap insulatinglayer 171 enables a nonvolatile threshold modulation operation(including a memory function) to be performed. That is, thesemiconductor element 200 having the function of a transistor having achangeable threshold can be formed. Moreover, the insulating film 212enables the nonvolatile threshold modulation operation (including thememory function) to be stably performed even at a higher temperature.Furthermore, since the tunnel insulating film (insulating film 212) isformed on the side of the channel (semiconductor layer 220) where theback gate 210 is provided, it is possible to implement a nonvolatilethreshold modulation operation characteristic without involving a changein the gate capacitance of the in-wiring-layer active element(component) (semiconductor element 200).

Tenth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the tenth embodiment. FIG. 25 is a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. FIG. 26 is a plan view showing theexample of the configuration of the semiconductor device according tothe present embodiment. Note that FIG. 25 is a cross section along theline A-A′ of FIG. 26. The semiconductor device of the present embodimentis different from the semiconductor device of the eighth embodiment(FIG. 22) in having a charge retaining layer. Hereinbelow, a descriptionwill be given mainly of the difference therebetween.

In the present embodiment, the semiconductor element 200 furtherincludes an insulating film 213 having a charge retaining functionbetween the back-gate insulating film 212 under the semiconductor layer220 and the back gate 211 coupled to the upper portion of the via 268.The semiconductor layer 220, the back-gate insulating film 212 incontact with the lower side of the semiconductor layer 220, theinsulating film 213 in contact with the lower side of the back-gateinsulating film 212, and the back gate 211 in contact with the lowerside of the insulating film 213 have the same shape (island shape) inplanar view. The sidewalls 226 cover the side surfaces of thesemiconductor layer 220, the back-gate insulating film 212, theinsulating film 213, and the back gate 211. In this case, the back gate211 can also be regarded as a control gate (or control electrode) whichcontrols the entrance/exit of charges. The gate electrode 222 can alsobe regarded as a read gate (or read gate electrode) which performs datareading.

Such a configuration can be implemented by the following steps. In themanufacturing method of the semiconductor device according to the eighthembodiment, over the second wire 186, the via 268, and the firstinterlayer insulating layer 152, the back gate 211 is formed by, e.g., asputtering method, the insulating film 213 and the back-gate insulatingfilm 212 are formed by, e.g., a CVD method, and the semiconductor layer220 is formed by, e.g., a sputtering method. Then, the laminate film ofthe back gate 211, the insulating film 213, the back-gate insulatingfilm 212, and the semiconductor layer 220 is patterned into an islandshape using typical photolithography and dry etching. The subsequentsteps are the same as in the steps of FIGS. 21D to 21G.

In the present embodiment also, the same effects as achieved in theeighth embodiment can be achieved.

In addition, in the present embodiment, the same semiconductor element200 as in the ninth embodiment can be formed even in an aluminum (Al)wiring layer. That is, the present embodiment can also achieve theeffects of the ninth embodiment resulting from the addition of the filmhaving the charge retaining function. As a result, an in-wiring-layeractive element (component) capable of a nonvolatile threshold modulationoperation (including a memory function) can be incorporated in thesemiconductor device according to the same design without depending onthe generation of the semiconductor device.

Eleventh Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the eleventh embodiment. FIG. 1s a cross-sectional viewshowing an example of the configuration of the semiconductor deviceaccording to the present embodiment. The semiconductor device of thepresent embodiment is different from the semiconductor device of thetenth embodiment (FIG. 25) in that the positions of the gate electrode222, the gate insulating film 221, the semiconductor layer 220, theback-gate insulating film 212, the insulating film 213, and the backgate 211 are vertically reversed. Hereinbelow, a description will begiven mainly of the difference therebetween.

The semiconductor element 200 of each of the tenth embodiment and thepresent embodiment is an in-wiring-layer active element (component)capable of a nonvolatile threshold modulation operation (including amemory function). However, in the semiconductor element 200 of the tenthembodiment, the gate insulating film 221 under the gate electrode 222 asthe top gate is thin and in contact with the semiconductor layer 220 tohave a large gate capacitance, while the insulating film 213 over theback gate 211 as the bottom gate has the charge retaining function andis in contact with the semiconductor layer 220 via the back-gateinsulating film 212. On the other hand, in the semiconductor element 200of the present embodiment, the gate electrode 222 and the gateinsulating film 221 serve as the bottom gate which is in contact withthe semiconductor layer 220, while the gate electrode 211 and theinsulating film 213 serve as the top gate which is in contact with thesemiconductor layer 220 via the gate insulating film 212. That is, thefunctions of the top gate and the bottom gate in the tenth embodimentare reversed in the present embodiment. In this case, the top-side gateelectrode 211 can also be regarded as a control gate (or a controlelectrode) which controls the entrance/exit of charges. On the otherhand, the back-side gate electrode 222 can also be regarded as a readgate (or a read gate electrode) which performs data reading.

Such a configuration can be implemented by reversing the order in whichthe individual films forming a gate stack are laminated in themanufacturing method of the semiconductor device of the tenthembodiment. In this manner, the semiconductor device according to thepresent embodiment (semiconductor device including the in-wiring-layeractive element (component) capable of the nonvolatile thresholdmodulation operation (including the memory function)) is formed in whichthe functions of the top gate and the bottom gate are reverse to thosein the semiconductor device of the tenth embodiment.

In the present embodiment, the same effects as obtained in the tenthembodiment can be obtained.

In addition, in the present embodiment, the area of the insulating film213 having the function of the charge retaining layer is reduced toallow the operations of injecting, retaining, and releasing charges tobe performed more stably.

Twelfth Embodiment

A description will be given of a configuration of a semiconductor deviceaccording to the twelfth embodiment. FIG. 28 is a layout chartschematically showing an example of the configuration of thesemiconductor device according to the twelfth embodiment. The drawingshows the layout of a semiconductor element over a wiring layer.Accordingly, in the drawing, the layout of the semiconductor element inthe surface region of the semiconductor substrate 101 which is providedbelow the wiring layer is omitted.

The semiconductor device of the present embodiment is a semiconductorchip 10. An example is shown in which, in the semiconductor chip 10, thesemiconductor element 200 of any of the first to eleventh embodiments isdisposed at any place. The semiconductor chip 10 includes a nonvolatilememory region 11, a dynamic threshold modulation region 12, a normallogic region 13, a double-gate logic operation region 14, a switchregion for reconfigurable logic circuit 15, a high-breakdown-voltageregion 16, and an access transistor/DRAM/ReRAM region 17.

In the nonvolatile memory region 11, for example, the semiconductorelement 200 of any of the ninth to eleventh embodiments can be used as anonvolatile memory. In the dynamic threshold modulation region 12, thesemiconductor element 200 of any of the ninth to eleventh embodimentscan be used as a transistor subjected to dynamic threshold voltagemodulation. In the normal logic region 13, of the semiconductor elements200 of the ninth to eleventh embodiments, one having the thresholdvoltage thereof set at a low level can be used as a transistor for a lowthreshold voltage region (LVt region) 21, one having the thresholdvoltage thereof set at a middle level can be used as a transistor for amiddle threshold voltage region (MVt region) 22, and one having thethreshold voltage thereof set at a high level can be used as atransistor for a high threshold voltage region (HVt region) 23. In thedouble-gate logic operation region 14, the semiconductor element of anyof the third and eighth to eleventh embodiments can be used as adouble-gate transistor. In the switch region for reconfigurable logiccircuit 15, the semiconductor element 200 of any of the first toeleventh embodiments can be used as a switch for switching a logiccircuit using the semiconductor element in the surface region of thesemiconductor substrate 101. In the high-breakdown-voltage region 16,the semiconductor element 200 of any of the modification of the secondembodiment and the ninth to eleventh embodiments can be used as atransistor for a high breakdown voltage. In the accesstransistor/DRAMM/ReRAM region 17, the semiconductor element 200 of anyof the first to eleventh embodiments can be used as an access transistorfor a DRAM (Dynamic Random Access Memory) or a ReRAM (Resistance RandomAccess Memory).

A manufacturing method of the semiconductor device of the presentembodiment is as described above in each of the embodiments.

In the present embodiment, the effects of the semiconductor devices ofthe individual embodiments used herein can be achieved.

In addition, in the present embodiment, particularly by thesemiconductor element 200 of each of the ninth to eleventh embodiments,a nonvolatile threshold adjusting function can be implemented. Thisallows the semiconductor elements 200 of the foregoing semiconductorchip 10 to be implemented with one type of element in the same wiringlayer. It is also possible to form a region not having a chargeretaining film.

Some or all of the foregoing embodiments and modifications can also bedescribed as in the following notes, but are not limited to thefollowing.

(Note 1) A semiconductor device, including: a first wiring layer havinga first interlayer insulating layer and a first wire embedded in thefirst interlayer insulating layer; a second wiring layer having a secondinterlayer insulating layer formed above the first wiring layer and asecond wire embedded in the second interlayer insulating layer; and asemiconductor element provided at least in the second wiring layer,wherein the semiconductor element includes: a semiconductor layerprovided in the second wiring layer; a first gate insulating filmprovided in contact with the semiconductor layer; a first gate electrodeprovided on the opposite side of the semiconductor layer via the firstgate insulating film; and a first side wall film provided over a sidesurface of the semiconductor layer.

(Note 2)

In a semiconductor device according to Note 1, the first gate electrodeextends from over the semiconductor layer beyond the first side wallfilm.

(Note 3)

In a semiconductor device according to Note 1, a material of thesemiconductor layer is an oxide semiconductor.

(Note 4)

In a semiconductor device according to Note 1, the semiconductor elementfurther includes a hard mask provided over the first gate electrode.

(Note 5)

In a semiconductor device according to Note 1, the semiconductor elementfurther includes: a second side wall film provided over a side surfaceof the first gate electrode.

(Note 6)

In a semiconductor device according to Note 5, an etching rate of amaterial of the second side wall film is different from an etching rateof a material of the second interlayer insulating layer.

(Note 7)

In a semiconductor device according to Note 6, a material of the secondinterlayer insulating layer includes a silicon oxide, and a material ofthe second side wall film includes a silicon nitride.

(Note 8)

In a semiconductor device according to Note 1, the semiconductor elementincludes first vias as a source electrode and a drain electrode, and thefirst via as the drain electrode is disposed at a predetermined distancefrom the gate electrode.

(Note 9)

In a semiconductor device according to Note 1, the semiconductor elementfurther includes: a second gate insulating film provided in contact withthe semiconductor layer on the opposite side of the first gateinsulating film with respect to the semiconductor layer; and a secondgate electrode provided in contact with the second gate insulating filmon the opposite side of the first gate electrode with respect to thesemiconductor layer.

(Note 10)

In a semiconductor device according to Note 9, the second gate is thefirst wire or a metal coupled to the first wire.

(Note 11)

In a semiconductor device according to Note 10, a region where thesecond gate electrode is formed is a part of a region where thesemiconductor layer exists in planar view.

(Note 12)

In a semiconductor device according to Note 1, the first gate insulatingfilm is provided over an entire upper surface of the semiconductorlayer.

(Note 13)

In a semiconductor device according to Note 12, the first side wall filmis provided so as to further cover a side surface of the first gateinsulating film.

(Note 14)

In a semiconductor device according to Note 13, the first side wall filmis provided so as to further cover an upper surface of the first gateinsulating film.

(Note 15)

In a semiconductor device according to Note 1, the first gate electrodeincludes a metal film including not less than two layers.

(Note 16)

In a semiconductor device according to Note 15, the metal film in alayer under the first gate electrode is provided only over a portion ofthe first gate insulating film located over the semiconductor layer, andthe metal film in a layer over the first gate electrode is provided overthe first gate insulating film to have such a shape as to extend acrossthe semiconductor layer.

(Note 17)

In a semiconductor device according to Note 15, the metal film in thelayer under the first gate electrode contains a titanium nitride.

(Note 18)

In a semiconductor device according to Note 17, the metal film in thelayer over the first gate electrode contains aluminum (Al).

(Note 19)

In a semiconductor device according to Note 9, the semiconductor elementfurther includes: a first insulating film provided so as to come incontact with either one of the first gate insulating film and the secondgate insulating film, and the first or second gate insulating film incontact with the first insulating film or the first insulating film hasa charge retaining function.

(Note 20)

In a semiconductor device according to Note 19, the gate electrodecloser to the insulating film having the charge retaining function is acontrol electrode.

(Note 21)

In a semiconductor device according to Note 20, the control electrode isembedded in the first wiring layer.

(Note 22)

In a semiconductor device according to Note 21, the first wire is a Cuwire.

(Note 23)

In a semiconductor device according to Note 20, the control electrode iscoupled to the first wire through a via in the first wiring layer.

(Note 24)

In a semiconductor device according to Note 23, the first wire is an Alwire.

(Note 25)

In a semiconductor device according to Note 19, the insulating filmhaving the charge retaining function contains silicon and nitrogen.

(Note 26)

In a semiconductor device according to Note 19, the gate electrodecloser to the insulating film not having the charge retaining functionis a read gate electrode.

(Note 27)

In a semiconductor device according to Note 19, the insulating filmhaving the charge retaining function functions as a wire diffusionbarrier film in a region where the semiconductor element is absent.

(Note 28)

In a semiconductor device according to Note 19, the semiconductorelement has a threshold which is adjusted with a quantity of chargesinjected into the insulating film having the charge retaining function.

(Note 29)

A method of manufacturing a semiconductor device, including the stepsof: forming an island-shaped semiconductor layer over a wiring layerhaving a first wire; forming an insulating film so as to cover thesemiconductor layer and the wiring layer therewith; etching back theinsulating film to form a first side wall film covering a side surfaceof the semiconductor layer; and forming a gate insulating film and agate electrode in this order over the semiconductor layer, wherein thegate electrode is formed over the gate insulating film so as to extendover the semiconductor layer and the first side wall film.

While the invention achieved by the present inventors has beenspecifically described heretofore based on the embodiments thereof, thepresent invention is not limited thereto. It will be appreciated thatvarious changes and modifications can be made in the invention within ascope not departing from the gist thereof. Also, the techniquesdescribed in the individual embodiments and the modifications thereofare also applicable to other embodiments and modifications unless atechnical contradiction occurs.

What is claimed is:
 1. A semiconductor device, comprising: a firstwiring layer having a first interlayer insulating layer and a first wireembedded in the first interlayer insulating layer; a second wiring layerhaving a second interlayer insulating layer formed above the firstwiring layer and a second wire embedded in the second interlayerinsulating layer; and a semiconductor element provided at least in thesecond wiring layer, wherein the semiconductor element includes: asemiconductor layer provided in the second wiring layer; a first gateinsulating film provided in contact with the semiconductor layer; afirst gate electrode provided on the opposite side of the semiconductorlayer via the first gate insulating film; and a first side wall filmprovided over a side surface of the semiconductor layer.
 2. Asemiconductor device according to claim 1, wherein the first gateelectrode extends over and laterally across the semiconductor layer. 3.A semiconductor device according to claim 1, wherein a material of thesemiconductor layer includes an oxide semiconductor.
 4. A semiconductordevice according to claim 1, wherein the semiconductor element furtherincludes: a second side wall film provided over a side surface of thefirst gate electrode.
 5. A semiconductor device according to claim 1,wherein an etching rate of a material of the second side wall film isdifferent from an etching rate of a material of the second interlayerinsulating layer.
 6. A semiconductor device according to claim 1,wherein the semiconductor element includes first vias as a sourceelectrode and a drain electrode, and wherein the first via as the drainelectrode is disposed at a predetermined distance from the gateelectrode.
 7. A semiconductor device according to claim 1, wherein thesemiconductor element further includes: a second gate insulating filmprovided in contact with the semiconductor layer on the opposite side ofthe first gate insulating film with respect to the semiconductor layer;and a second gate electrode provided in contact with the second gateinsulating film on the opposite side of the first gate electrode withrespect to the semiconductor layer.
 8. A semiconductor device accordingto claim 7, wherein the second gate is the first wire or a metal coupledto the first wire.
 9. A semiconductor device according to claim 8,wherein a region where the second gate electrode is formed is a part ofa region where the semiconductor layer exists in planar view.
 10. Asemiconductor device according to claim 1, wherein the first gateinsulating film is provided over an entire upper surface of thesemiconductor layer.
 11. A semiconductor device according to claim 10,wherein the first side wall film is provided so as to further cover aside surface of the first gate insulating film.
 12. A semiconductordevice according to claim 11, wherein the first side wall film isprovided so as to further cover an upper surface of the first gateinsulating film.
 13. A semiconductor device according to claim 1,wherein the first gate electrode includes a metal film including notless than two layers.
 14. A semiconductor device according to claim 13,wherein the metal film in a layer under the first gate electrode isprovided only over a portion of the first gate insulating film locatedover the semiconductor layer, and wherein the metal film in a layer overthe first gate electrode is provided over the first gate insulating filmto have such a shape as to extend across the semiconductor layer.
 15. Asemiconductor device according to claim 7, wherein the semiconductorelement further includes: a first insulating film provided so as to comein contact with either one of the first gate insulating film and thesecond gate insulating film, and wherein the first or second gateinsulating film in contact with the first insulating film, or the firstinsulating film has a charge retaining function.
 16. A semiconductordevice according to claim 15, wherein the gate electrode closer to theinsulating film having the charge retaining function is a controlelectrode.
 17. A semiconductor device according to claim 16, wherein thecontrol electrode is embedded in the first wiring layer.
 18. Asemiconductor device according to claim 16, wherein the controlelectrode is coupled to the first wire through a via in the first wiringlayer.
 19. A semiconductor device according to claim 15, wherein thesemiconductor element has a threshold which is adjusted with a quantityof charges injected into the insulating film having the charge retainingfunction.
 20. A method of manufacturing a semiconductor device,comprising the steps of: forming an island-shaped semiconductor layerover a wiring layer having a first wire; forming an insulating film soas to cover the semiconductor layer and the wiring layer therewith;etching back the insulating film to form a first side wall film coveringa side surface of the semiconductor layer; and forming a gate insulatingfilm and a gate electrode in this order over the semiconductor layer,wherein the gate electrode is formed over the gate insulating film so asto extend over the semiconductor layer and the first side wall film.